1. Field of the Invention
The present invention relates to a resin composition for a moisture absorbing film, to a moisture absorbing film for a package, and to a method for manufacturing same, the resin composition comprising polyethylene resin and polyacrylic acid partial sodium salt (PAPSS) or attapulgite synthesized acrylamide (ATPGAA) as a moisture absorbent.
2. Description of the Related Art
According to the recent development of modern industry, diversification and merchantability of products are considered to be important. In production, storage, distribution and sale of products, the consumer demand for handling convenience and quality preservation is growing.
Therefore, there is active research effort in the field of packaging industry to improve marketability of products to give functional factor(s) and to provide active effects into the product packaging, away from the conventional simple purpose of package protection and quality maintenance.
Nowadays, plastic packaging materials of foods, medicines, electronics and household goods have actively developed due to the lightweight, excellent gas barrier properties, transparency, and relatively low cost of plastic packaging.
Functional packaging materials in recent research mostly are produced by impregnation and coating of the packaging materials with active substances to improve the quality of products by consistently providing the products with maximum effect from the time of packaging. For example, there have been attempts to develop films such as nano-film for increasing moisture and gas barrier properties, film comprising zeolite for inhibiting growth of microorganisms of the products, far infrared radiation film emitting energy, off-flavor-adsorptive film, and oxygen and/or off-flavor gas-adsorptive film.
If food is moisture sensitive, there is a need for the insides of the packaging to remain dry because water activity is one of the factors which induce changes in the physical properties of product, occurrence of rancidity, loss of nutritional value, decrease of sensual properties, and food deterioration through microbial growth. Water activity may be also one of the factors to decrease the quality of the packaged products by inducing oxidation corrosion of a metal surface in the electronic products.
In order to solve these problems, food is typically treated with hot air-drying pretreatment, drying gas substitution packaging, blockable vacuum packaging, desiccant addition to inside the packaging and the like. However, these methods are disadvantageous such as inconvenient processing, increased cost, weakening of drying durability through increasing storage period.
Desiccant is one of the substances used to remove moisture from the material to be dry. Desiccants react with water, and eliminates it by a chemical action of adhering moisture, or by a physical action of water-adsorption or water-absorption, separately. Typical desiccants which remove moisture by chemical action are calcium chloride or copper sulfate, and these desiccants absorb moisture in the form of crystal water. Typical desiccants which remove moisture by physical action are silica-gel, aluminium oxide, zeolite, and the like, and these are able to accommodate a large amount of moisture in the large surface area of the material.
As one of these desiccants, silica-gel is a granular mineral material of silicon dioxide (SiO2). The average pore size of silica-gel as a desiccant is 24 Å, and it has a high affinity with water molecules. Silica-gel has a property to pull moisture until 220° F. (105° C.), shows maximum activity as a desiccant in the range of 70° F.˜90° F., 60˜90% RH, and absorb moisture by 40% RH. It is the only approved material in the FDA (U.S.A.) which can directly come in contact with foods and medicines.
Silica-gel can absorb many organic chemical materials other than water, and has various pore sizes. The silica-gel's absorbable chemical materials in the order of absorbability are as follows: water, ammonia, alcohols, aromatics, diolefins, olefins, and paraffins.
As an another desiccant, molecular sieve is a synthetic porous aluminosilicate having strong moisture-adsorbing capacity. Unlike other desiccants, the adsorbing pores of molecular sieve are uniformed and lattice structured. The size of the adsorbing pores can be controlled. In general, molecular sieves having 3 Å, 4 Å, 5 Å, 10 Å adsorbing pores are used.
Molecular sieve can adsorb water, but emits volatile substances. In case of 3 Å, water is adsorbed and many hydrocarbons are emitted. In case of 4 Å, the adsorption capacity is superior than that of 3 Å, but emits more buthane. It can contain moisture up to 230° C. (450° F.) and can maintain up to 10% RH since it has better moisture adsorbing capacity than silica-gel. The FDA has not approved sodium aluminosilicate for direct contact with consumable items, but the use of molecular sieves is allowed in Europe for pharmaceuticals. It is expensive, but adsorption capacity is excellent, and thus it is generally used to maintain low humidity conditions.
As the other desiccant, montmorillonite (MMT) clay is prepared by drying magnesium aluminum silicate in a form of sub-bentonite. If there is not any contamination and swelling, MMT once used under low humidity condition can be re-cycled. It has shown a reverse effect of re-emission water after absorbing it. MMT performs the desiccant function in the temperature condition of 120° F. (50° C.) or less, while it emits water rather than absorbing it in temperatures above 120° F. (50° C.). Therefore, when MMT is used as a desiccant, considerations must be given to the storage and distribution conditions. In general, at the standard relative humidity at room temperature, it fully functions as a desiccant. The color of MMT particle is gray, and the purity thereof should be increased to minimize any reaction with the packaging products.
Calcium oxide (CaO) can absorb water up to 28.5 wt % of its own weight. Since CaO has excellent absorbing capacity among the desiccants, it is used when maintaining the condition of low humidity is very important. CaO absorbs moisture at a slow pace, and swells by the absorbed moisture. In case of dry-frozen food, the use of CaO is limited.
The desiccants such as CaO, zeolite, and silica-gel have been used in the way of putting one of them in a Tyvek pouch, sealing the pouch, and applying it into food packages.
The basic objectives of using desiccants are to maintain the original texture of the products and to block any microbial growth in them. In case of fruits, desiccants prevent the fruits from producing water droplets due to the water vapors of fruit transpiration by adjusting saturated humidity conditions in fruit packages.
Salts, saturated salt solution, or superabsorbent polymer can be mainly used as a desiccant, and superabsorbent polymer sheet usually is used in meat or fish products to absorb meat or fish broth produced depending on the temperature. Polyacrylate or starch graft polymer is mainly used as the sheet material. In these cases, packaging products incorporated huectant between the plastic films, such as propylene glycol (film) sealing with polyvinyl alcohol, can be used for the purpose of covering meat or fish. It also can be applied to protect electronic products or components, and metal/electrical, or electronic precision machines by preventing rust or corrosion that may occur from their contact with moisture during storage or transportation.
Desiccants are widely used to maintain the quality of food, medicine, electronic product, and the like. The desiccant is usually used as a form of small pouch, and it is packaged together with the product inside the packaging. Thus, there may be some concerns of contamination of food or of diminishing the quality of the products. There may be deficiencies in the packaging pouch, and the spilled desiccant may cause adverse effects to consumers' safety when the desiccant is used for food or medicine.
Also, the process of putting desiccant pouches into the product is inconvenient, and it is highly possible that the desiccant will produce off-flavor and/or reactants after adsorbing moisture.
Therefore, the inventors of the present invention intended to develop a functional adsorbing packaging film for moisture-sensitive products with consideration for handy uses and long lasting effect of moisture-adsorption. Various desiccants were investigated and selected for their high moisture-adsorption capabilities, and samples were prepared and analyzed in a desiccant impregnated form into the plastic films by concentration of the desiccant. Physical properties and functional adsorption effect of the impregnated film were tested.
As a result, the present invention is completed by identifying that when a film is manufactured from polyethylene resin impregnated with polyacrylic acid partial sodium salt (PAPSS) or attapulgite synthesized acrylamide (ATPGAA), it provides excellent moisture adsorbing capability and good physical properties.
The present invention also provides film with resin composition to be used conveniently and having a long lasting-adsorption capacity for packaging moisture-sensitive dried food such as laver.